The present invention generally relates to the field of acoustic communications, and more particularly to a system which selectively transmits acoustic energy in the audible and/or ultrasonic frequency ranges based on predetermined criteria.
Virtually all commercial and military ships have public address systems that are deliberately designed to be very loud so that the messages they convey are intelligible. However, in some applications, such as in high noise environments or in radio silence operating modes, it is desirable to operate the audio communication systems so that messages are essentially undetectable by unauthorized persons, but where in other applications using the same systems, it is desirable for the messages to be detected by many persons. Therefore, a need exists for an audio communication system that can be operated in a public address mode so that audio messages may be broadcast to many persons, and/or in an ultrasonic confidential mode so that messages may only be detected by specially designated individuals.